Well operations system

ABSTRACT

Abstract of the Disclosure 
         
   A wellhead has, instead of a conventional Christmas tree, a spool tree (34) in which a tubing hanger (54) is landed at a predetermined angular orientation.  As the tubing string can be pulled without disturbing the tree, many advantages follow, including access to the production casing hanger (21) for monitoring production casing annulus pressure, and the introduction of larger tools into the well hole without breaching the integrity of the well.

Detailed Description of the Invention Detailed Description

[0001] This is a divisional application of copending application serial number 09/657,018 filed September 7, 2000 which is a continuation of application serial number 09/092,549 filed June 5, 1998 which is a divisional continuing application of serial number 08/679,560 filed July 12, 1996, now U.S. Patent 6,039,119, which is a continuation of serial number 08/204,397 filed March 16, 1994, now U.S. Patent 5,544,707, which claims the benefit of PCT application PCT/US93/05246 filed on May 28, 1993, which claims the priority of European Patent Office application 92305014 filed on June 1, 1992, all of the above hereby incorporated herein by reference.

[0002] Conventionally, wells in oil and gas fields are built up by establishing a wellhead housing, and with a drilling blow out preventer stack (BOP) installed, drilling down to produce the well hole whilst successively installing concentric casing strings, which are cemented at the lower ends and sealed with mechanical seal assemblies at their upper ends. In order to convert the cased well for production, a tubing string is run in through the BOP and a hanger at its upper end landed in the wellhead. Thereafter the drilling BOP stack is removed and replaced by a Christmas tree having one or more production bores containing actuated valves and extending vertically to respective lateral production fluid outlet ports in the wall of the Christmas tree.

[0003] This arrangement has involved problems which have, previously, been accepted as inevitable. Thus any operations down hole have been limited to tooling which can pass through the production bore, which is usually no more than five inch diameter, unless the Christmas tree is first removed and replaced by a BOP stack. However this involves setting plugs or valves, which may be unreliable by not having been used for a long time, down hole. The well is in a vulnerable condition whilst the Christmas tree and BOP stack are being exchanged and neither one is in position, which is a lengthy operation. Also, if it is necessary to pull the completion, consisting essentially of the tubing string on its hanger, the Christmas tree must first be removed and replaced by a BOP stack. This usually involves plugging and/or killing the well.

[0004] A further difficulty which exists, particularly with subsea wells, is in providing the proper angular alignment between the various functions, such as fluid flow bores, and electrical and hydraulic lines, when the wellhead equipment, including the tubing hanger, Christmas tree, BOP stack and emergency disconnect devices are stacked up. Exact alignment is necessary if clean connections are to be made without damage as the devices are lowered into engagement with one another. This problem is exacerbated in the case of subsea wells as the various devices which are to be stacked up are run down onto guide posts or a guide funnel projecting upwardly from a guide base. The post receptacles which ride down on to the guide posts or the entry guide into the funnel do so with appreciable clearance. This clearance inevitably introduces some uncertainty in alignment and the aggregate misalignment when multiple devices are stacked, can be unacceptably large. Also the exact orientation will depend upon the precise positions of the posts or keys on a particular guide base and the guides on a particular running tool or BOP stack and these will vary significantly from one to another. Consequently it is preferable to ensure that the same running tools or BOP stack are used for the same wellhead, or a new tool or stack may have to be specially modified for a particular wellhead. Further misalignments can arise from the manner in which the guide base is bolted to the conductor casing of the wellhead.

[0005] In accordance with the present invention, a wellhead comprises a wellhead housing; a spool tree fixed and sealed to the housing, and having at least a lateral production fluid outlet port connected to an actuated valve; and a tubing hanger landed within the spool tree at a predetermined angular position at which a lateral production fluid outlet port in the tubing hanger is in alignment with that in the spool tree.

[0006] With this arrangement, the spool tree, takes the place of a conventional Christmas tree but differs therefrom in having a comparatively large vertical through bore without any internal valves and at least large enough to accommodate the tubing completion. The advantages which are derived from the use of such spool tree are remarkable, in respect to safety and operational benefits.

[0007] Thus, in workover situations the completion, consisting essentially of the tubing string, can be pulled through a BOP stack, without disturbing the spool tree and hence the pressure integrity of the well, whereafter full production casing drift access is provided to the well through the large bore in the spool tree. The BOP can be any appropriate workover BOP or drilling BOP of opportunity and does not have to be one specially set up for that well.

[0008] Preferably, there are complementary guide means on the tubing hanger and spool tree to rotate the tubing hanger into the predetermined angular position relatively to the spool tree as the tubing hanger is lowered on to its landing. With this feature the spool tree can be landed at any angular orientation onto the wellhead housing and the guide means ensures that the tubing string will rotate directly to exactly the correct angular orientation relatively to the spool tree quite independently of any outside influence. The guide means to control rotation of the tubing hanger into the predetermined angular orientation relatively to the spool tree may be provided by complementary oblique edge surfaces one facing downwardly on an orientation sleeve depending from the tubing hanger the other facing upwardly on an orientation sleeve carried by the spool tree.

[0009] Whereas modern well technology provides continuous access to the tubing annulus around the tubing string, it has generally been accepted as being difficult, if not impossible, to provide continuous venting and/or monitoring of the pressure in the production casing annulus, that is the annulus around the innermost casing string. This has been because the production casing annulus must be securely sealed whist the Christmas tree is fitted in place of the drilling BOP, and the Christmas tree has only been fitted after the tubing string and hanger has been run in, necessarily inside the production casing hanger, so that the production casing hanger is no longer accessible for the opening of a passageway from the production casing annulus. However, the new arrangement, wherein the spool tree is fitted before the tubing string is run in provides adequate protected access through the BOP and spool tree to the production casing hanger for controlling a passage from the production casing annulus.

[0010] For this purpose, the wellhead may include a production casing hanger landed in the wellhead housing below the spool tree; an isolation sleeve which is sealed at its lower end to the production casing hanger and at its upper end to the spool tree to define an annular void between the isolation sleeve and the housing; and an adapter located in the annular space and providing part of a passage from the production casing annulus to a production casing annulus pressure monitoring port in the spool tree, the adapter having a valve for opening and closing the passage, and the valve being operable through the spool tree after withdrawal of the isolation sleeve up through the spool tree. The valve may be provided by a gland nut, which can be screwed up and down within a body of the adapter to bring parts of the passage formed in the gland nut and adapter body, respectively, into and out of alignment with one another. The orientation sleeve for the tubing hanger may be provided within the isolation sleeve.

[0011] Production casing annulus pressure monitoring can then be set up by method of completing a cased well in which a production casing hanger is fixed and sealed by a seal assembly to a wellhead housing, the method comprising, with BOP installed on the housing, removing the seal assembly and replacing it with an adapter which is manipulatable between configurations in which a passages from the production casing annulus up past the production casing hanger is open or closed; with the passage closed, removing the BOP and fitting to the housing above the production casing hanger a spool tree having an internal landing for a tubing hanger; installing a BOP on the spool tree; running a tool down through the BOP and spool tree to manipulate the valve and open the passage; inserting through the BOP and spool tree an isolation sleeve, which seals to both the production casing and spool tree and hence defines between the sleeve and casing an annular void through which the passage leads to a production caning annulus pressure monitoring port in the spool tree; and running a tubing string down through the BOP and spool tree until the tubing hanger lands in the spool tree with lateral outlet ports in the tubing hanger and spool tree for production fluid flow, in alignment with one another.

[0012] According to a further feature of the invention the spool tree has a downwardly depending location mandrel which is a close sliding fit within a bore of the wellhead housing. The close fit between the location mandrel of the spool tree and the wellhead housing provides a secure mounting which transmits inevitable bending stresses to the housing from the heavy equipment, such as a BOP, which projects upwardly from the top of the wellhead housing, without the need for excessively sturdy connections. The location mandrel may be formed as an integral part of the body of the spool tree, or may be a separate part which is securely fixed, oriented and sealed to the body.

[0013] Pressure integrity between the wellhead housing and spool tree may be provided by two seals positioned in series one forming an environmental seal (such as an AX gasket) between the spool tree and the wellhead housing, and the other forming a production seal between the location mandrel and either the wellhead housing or the production casing hanger.

[0014] During workover operations, the production casing annulus can be resealed by reversing the above steps, if necessary after setting plugs or packers down hole.

[0015] When production casing pressure monitoring is unnecessary, so that no isolation sleeve is required, the orientation sleeve carried by the spool tree for guiding and rotating the tubing hanger down into the correct angular orientation may be part of the spool tree location mandrel itself.

[0016] Double barrier isolation, that is to say two barriers in series, are generally necessary for containing pressure in a well. If a spool tree is used instead of a conventional Christmas tree, there are no valves within the vertical production and annulus fluid flow bores within the tree, and alternative provision must be made for sealing the bore or bores through the top of the spool tree which provide for wire line or drill pipe access.

[0017] In accordance with a further feature of the invention, at least one vertical production fluid bore in the tubing hanger is sealed above the respective lateral production fluid outlet port by means of a removable plug, and the bore through the spool tree being sealed above the tubing hanger by means of a second removable plug.

[0018] With this arrangement, the first plug, takes the function of a conventional swab valve, and may be a wireline set plug. The second plug could be a stopper set in the spool tree above the tubing hanger by, e.g., a drill pipe running tool. The stopper could contain at least one wireline retrievable plug which would allow well access when only wire line operations are called for. The second plug should seal and be locked internally into the spool tree as it performs a barrier to the well when a BOP or intervention module is deployed. A particular advantage of this double plug arrangement is that, as is necessary to satisfy authorities in some jurisdictions, the two independent barriers are provided in mechanically separate parts, namely the tubing hanger and its plug and the second plug in the spool tree.

[0019] A further advantage arises if a workover port extends laterally through the wall of the spool tree from between the two plugs; a tubing annulus fluid port extends laterally through the wall of the spool tree from the tubing annulus; and these two ports through the spool tree are interconnected via an external flow line containing at least one actuated valve. The bore from the tubing annulus can then terminate at the port in the spool tree and no wireline access to the tubing annulus bore is necessary through the spool tree as the tubing annulus bore can be connected via the interplug void to choke or kill lines, i.e. a BOP annulus, so that downhole circulation is still available. It is then only necessary to provide wireline access at workover situations to the production bore or bores. This considerably simplifies workover BOP and/or riser construction. When used in conjunction with the plug at the top of the spool tree, the desirable double barrier isolation is provided by the spool tree plug over the tubing hanger, or workover valve from the production flow.

[0020] When the well is completed as a multi production bore well, in which the tubing hanger has at least two vertical production through bores each with a lateral production fluid flow port aligned with the corresponding port in the spool tree, at least two respective connectors may be provided for selective connection of a single bore wire line running tool to one or other of the production bores, each connector having a key for entering a complementary formation at the top of the spool tree to locate the connector in a predetermined angular orientation relatively to the spool tree. The same type of alternative connectors may be used for providing wireline or other running tool access to a selected one of a plurality of functional connections, e.g. electrical or hydraulic couplings, at the upper end of the tubing hanger.

[0021] The development and completion of a subsea wellhead in accordance with the present invention are illustrated in the accompanying drawings, in which:

[0022] Figures 1 to 8 are vertical axial sections showing successive steps in development and completion of the wellhead, the Figure numbers bearing the letter A being enlargements of part of the corresponding Figures of same number without the A:

[0023]Figure 9 is a circuit diagram showing external connections to the spool 3;

[0024]Figure 10 is a vertical axial section through a completed dual production bore well in production mode;

[0025] Figures 11 and 12 are vertical axial sections showing alternative connectors to the upper end of the dual production bore wellhead during work over; and,

[0026]Figure 13 is a detail showing the seating of one of the connectors in the spool tree.

[0027]Figure 1 shows the upper end of a cased well having a wellhead housing 20, in which casing hangers, including an uppermost production casing hanger 21 for, for example, 9 5/8" or 10 3/4", production casing is mounted in conventional manner. Figure 1 shows a conventional drilling BOP 22 having rams 23 and kill and choke lines 24 connected to the upper end of the housing 20 by a drilling connector 25.

[0028] As seen in more detail in Figure 1A, the usual mechanical seal assemblies between the production casing hanger 21 and the surrounding wellhead housing 20 have been removed and replaced through the BOP with an adapter 26 consisting of an outer annular body part 27 and an inner annular gland nut 28 which has a screw threaded connection to the body 27 so that it can be screwed between a lowered position shown on the right hand side of Figure 1A, in which radial ducts 29 and 30, respectively in the body 27 and nut 28, are in communication with one another, and a raised position shown on the left hand side of Figure 1A, in which the ducts are out of communication with one another. The duct 29 communicates through a conduit 31 between a depending portion of the body 27 and the housing 20, and through a conduit 32 passing through the production casing hanger 21, to the annulus surround the production casing. The duct 30 communicates through channels 33 formed in the radially inner surface of the nut 28, and hence to a void to be described. The cooperation between the gland nut 28 and body 27 of the adapter therefore acts as a valve which can open and close a passage up past the production casing hanger from the production casing annulus. After appropriate testing, a tool is run in through the BOP and, by means by radially projecting spring lugs engaging in the channels 33, rotates the gland nut 28 to the valve closed position shown on the right hand side on Figure 1A. The well is thus resealed and the drilling BOP 22 can temporarily be removed.

[0029] As shown in Figures 2 and 2A, the body of a tree spool 34 is then lowered on a tree installation tool 35, using conventional guide post location, or a guide funnel in case of deep water, until a spool tree mandrel 36 is guided into alignment with and slides as a close machined fit, into the upper end of the wellhead housing 20, to which the spool tree is then fixed via a production connector 37 and bolts 48. The mandrel 36 is actually a separate part which is bolted and sealed to the rest of the spool tree body. As seen particularly in Figure 2A a weight set AX gasket 39, forming a metal to metal environmental seal is provided between the spool tree body and the wellhead housing 20. In addition two sets of sealing rings 40 provide, in series with the environmental seal, a production fluid seal externally between the ends to the spool tree mandrel 36 to the spool tree body and to the wellhead housing 20. The intervening cavity can be tested through a test part 40A. The provision of the adapter 26 is actually optional, and in its absence the lower end of the spool tree mandrel 36 may form a production seal directly with the production casing hanger 21. As is also apparent from reasons which will subsequently become apparent, the upper radially inner edge of the spool tree mandrel projects radially inwardly from the inner surface of the spool tree body above, to form a landing shoulder 42 and at least one machined key slot 43 is formed down through the landing shoulder.

[0030] As shown in Figure 3, the drilling BOP 22 is reinstalled on the spool tree 34. The tool 44 used to set the adapter in Figure 1, having the spring dogs 45, is again run in until it lands on the shoulder 42, and the spring dogs 45 engage in the channels 33. The tool is then turned to screw the gland nut 28 down within the body 27 of the adapter 26 to the valve open position shown on the right hand side in Figure 1A. It is now safe to open the production casing annulus as the well is protected by the BOP.

[0031] The next stage, show in Figures 4 and 4A, is to run in through the BOP and spool tree on an appropriate tool 44A a combined isolation and orientation sleeve 45. This lands on the shoulder 42 at the top of the spool tree mandrel and is rotated until a key on the sleeve drops into the mandrel key slot 43. This ensures precise angular orientation between the sleeve 45 and the spool tree 44, which is necessary, and in contrast to the angular orientation between the spool tree 34 and the wellhead casing, which is arbitrary. The sleeve 45 consists of an external cylindrical portion, an upper external surface of which is sealed by ring seals 46 to the spool tree 34, and the lower external surface of which is sealed by an annular seal 47 to the production casing hanger 21. There is thus provided between the sleeve 45 and the surrounding wellhead casing 20 a void 48 with which the channels 33, now defined radially inwardly by the sleeve 45, communicate. The void 48 in turn communicates via a duct 49 through the mandrel and body of the spool tree 34 to a lateral port. It is thus possible to monitor and vent the pressure in the production casing annulus through the passage provided past the production casing hanger via the conduits 32, 31 the ducts 29 and 30, the channels 33, shown in Figure 1A, the void 48, the duct 49, and the lateral port in the spool tree. In the drawings, the radial portion of the duct 49 is shown apparently communicating with a tubing annulus, but this is draftsman's license and the ports from the two annuli are, in fact, angularly and radially spaced.

[0032] Within the cylindrical portion of the sleeve 45 is a lining, which may be fixed in the cylindrical portion, or left after internal machining of the sleeve. This lining provides an orientation sleeve having an upper/edge forming a cam 50. The lowermost portion of the cam leads into a key slot 51.

[0033] As shown in Figures 5, 6 and 6A a tubing string of production tubing 53 on a tubing hanger 54 is run in through the BOP 22 and spool tree 34 on a tool 55 until the tubing hanger lands by means of a keyed shoulder 56 on a landing in the spool tree and is locked down by a conventional mechanism 57. The tubing hanger 54 has a depending orientation sleeve 58 having an oblique lower edge forming a cam 59 which is complementary to the cam 50 in the sleeve 45 and, at the lower end of the cam, a downwardly projecting key 60 which is complementary to the key slot 51. The effect of the cams 50 and 59 is that, irrespective of the angular orientation of the tubing string as it is run in, the cams will cause the tubing hanger 54 to be rotated to its correct angular orientation relatively to the spool tree and the engagement of the key 60 in the key slot 51 will lock this relative orientation between the tubing hanger and spool tree, so that lateral production and tubing annulus fluid flow ports 61 and 62 in the tubing hanger 54 are in alignment with respective lateral production and tubing annulus fluid flow ports 63 and 64 through the wall of the spool tree. Metal to metal annulus seals 65, which are set by the weight of the tubing string, provide production fluid seals between the tubing hanger 54 and the spool tree 34. Provision is made in the top of the tubing hanger 54 for a wireline set plug 66. The keyed shoulder 56 of the tubing hanger lands in a complementary machined step in the spool tree 34 to ensure ultimate machined accuracy of orientation between the tubing hanger 54 and the spool tree 34.

[0034]Figure 7 shows the final step in the completion of the spool tree. This involves the running down on drill pipe 67 through the BOP, an internal isolation stopper 68 which seals within the top of the spool tree 34 and has an opening closed by an in situ wireline activated plug 69. The BOP can then be removed leaving the wellhead in production mode with double barrier isolation at the upper end of the spool tree provided by the plugs 66 and 69 and the stopper 68. The production fluid outlet is controlled by a master control valve 70 and pressure through the tubing annulus outlet ports 62 and 64 is controlled by an annulus master valve 71. The other side of this valve is connected, through a workover valve 72 to a lateral workover port 73 which extends through the wall of the spool tree to the void between the plugs 69 and 66. With this arrangement, wireline access to the tubing annulus in and downstream of a tubing hanger is unnecessary as any circulation of fluids can take place through the valves 71 and 72, the ports 62, 64 and 73, and the kill or choke lines of any BOP which has been installed. The spool tree in the completed production mode is shown in Figure 8.

[0035]Figure 9 shows valve circuitry associated with the completion and, in addition to the earlier views, shows a production fluid isolation valve 74, a tubing annulus valve 75 and a cross over valve 76. With this arrangement a wide variety of circulation can be achieved down hole using the production bore and tubing annulus, in conjunction with choke and kill lines extending from the BOP and through the usual riser string. All the valves are fail/safe closed if not actuated.

[0036] The arrangement shown in Figures 1 to 9 is a mono production bore wellhead which can be accessed by a single wireline or drill pipe, and the external loop from the tubing annulus port to the void between the two plugs at the top of the spools tree avoids the need for wireline access to the tubing annulus bore.

[0037]Figure 10 corresponds to Figure 8 but shows a 5-1/2 inch x 2-3/8 inch dual production bore wellhead with primary and secondary production tubing 53A and 53B. Development and completion are carried out as with the monobore wellhead except that the spool tree 34A and tubing hanger 54A are elongated to accommodate lateral outlet ports 61A, 63A for the primary production fluid flow from a primary bore 80 in the tubing hanger to a primary production master valve 70A, and lateral outlet ports 62A, 64A for the secondary production fluid flow from a secondary bore 81 in the tubing hanger to a secondary production master valve 70B. The upper ends of the bores 80 and 81 are closed by wireline plugs 66A and 66B. A stopper 68A, which closes the upper end of the spool tree 34A has openings, in alignment with the plugs 66A and 66B, closed by wireline plugs 69A and 69B.

[0038] Figures 11 and 12 show how a wireline 77 can be applied through a single drill pipe to activate selectively one or other of the two wireline plugs 66A and 66B in the production bores 80 and 81 respectively. This involves the use of a selected one of two connectors 82 and 83. In practice, a drilling BOP 22 is installed and the stopper 68A is removed. Thereafter the connector 82 or 83 is run in on the drill pipe or tubing until it lands in, and is secured and sealed to the spool tree 34A. Figure 13 shows how the correct angular orientation between the connector 82 or 83 and the spool tree 34A, is achieved by wing keys 84, which are guided by Y-shaped slots 85 in the upper inner edge of the spool tree, first to bring the connectors into the right angular orientation, and then to allow the relative axial movement between the parts to enable the stabbing function when the wireline connector engages with its respective pockets above plug 66A or 66B. To ensure equal landing forces and concentricity on initial contact, two keys 84A and 84B are recommended. As the running tool is slowly rotated under a new control weight, it is essential that the tool only enters in one fixed orientation. To ensure this key 84A is wider than key 84B and its respective Y-shaped slots. It will be seen that one of the connectors 82 has a guide duct 86 which leads the wireline to the plug 66B whereas the other connector 83 has a similar guide duct 87 which leads the wireline to the other plug 66A. 

What is Claimed is:
 1. 1-15. (Canceled)
 2. 16.An apparatus for creating a second fluid barrier for the sealed connection between a production mandrel and a wellhead supporting and sealed to a hanger, comprising: a member having first seals on one end and second seals on another end; said one end extending into the production mandrel with said first seals sealingly engaging the production mandrel; and said other end extending into the wellhead with said second seals sealingly engaging the hanger for isolating the hanger.
 3. 17.The apparatus of claim 16 wherein said member includes an orientation surface for orienting a tubing hanger within the production mandrel.
 4. 18.The apparatus of claim 17 further including an alignment member on said member for aligning said member within the production mandrel.
 5. 19.The apparatus of claim 16 wherein said member creates an annular void between said member and the wellhead.
 6. 20.The apparatus of claim 16 wherein said member includes a support on said one end for supporting said member within the production mandrel and said other end creates a sliding engagement with the hanger.
 7. 21.An apparatus for completing a well comprising: a wellhead supporting a hanger and a packing member for sealing said wellhead and hanger; a production member disposed on said wellhead and a metal-to-metal seal for sealing said production member and wellhead; an isolation member having first seals on one end and second seals on another end; said production member supporting said isolation member; said first seals sealingly engaging said production member; said hanger slidingly receiving said another end of said isolation member; and said second seals sealingly engaging said hanger for establishing a second seal to said metal-to-metal seal.
 8. 22.The apparatus of claim 21 wherein said isolation member creates an annular space between said isolation member and said wellhead.
 9. 23.The apparatus of claim 22 wherein said production member includes a fluid passageway extending from said annular space to an exterior of said production member.
 10. 24.The apparatus of claim 23 further including a test valve on said production member for controlling flow through said passageway.
 11. 25.The apparatus of claim 23 further including a second fluid passageway extending from said void to an annulus formed between said wellhead and hanger for monitoring or bleeding off fluid pressure in said annulus.
 12. 26.The apparatus of claim 25 further including an internal valve for controlling flow through said second fluid passageway.
 13. 27.The apparatus of claim 21 wherein said isolation member includes a bore therethrough having a diameter no smaller than the diameter of the flowbore of said hanger.
 14. 28.A method for completing a well comprising: lowering a hanger suspending casing into the well; supporting the hanger within a wellhead and creating a casing annulus; sealing the hanger and wellhead; connecting and sealing a production member to the wellhead forming a first fluid barrier; lowering an isolation member into the production member and wellhead; supporting and sealing the isolation member within the production member; slidingly receiving one end of the isolation member within the hanger; and sealing the isolation member and hanger thereby forming a second fluid barrier.
 15. 29.The method of claim 28 further including the step of supporting tubing within the production member and forming a third fluid barrier.
 16. 30.The method of claim 28 further including: creating a fluid passageway from the casing annulus and through a wall of the production member; and monitoring the fluid pressure in the casing annulus.
 17. 31.The method of claim 30 further including the step of bleeding fluid pressure through the fluid passageway.
 18. 32.A flow completion system for controlling the flow of fluid from a well bore, the flow completion system comprising: a tubing spool which includes a central bore that extends axially therethrough and a production outlet which communicates with the central bore; a tubing hanger assembly which is supported in the central bore and which includes a production bore that extends axially therethrough and a production passageway that communicates between the production bore and the production outlet, the tubing hanger assembly supporting a tubing string which extends into the well bore and defines a tubing annulus surrounding the tubing string; a first closure member positioned in the production bore above the production passageway; a first seal positioned between the tubing hanger assembly and the tubing spool above the production passageway; wherein the first closure member and the first seal comprise a first pressure-containing barrier between the well bore and a surrounding environment; a second closure member which is positioned in the production bore above the first closure member; and a second seal which is disposed on the tubing hanger assembly and positioned within the tubing spool above the first seal; wherein the second closure member and the second seal comprise a second pressure-containing barrier between the well bore and the environment; and wherein both the first and the second barriers are associated with the tubing hanger assembly.
 19. 33.The flow completion system of claim 32 wherein the tubing hanger assembly includes a tubing hanger and a seal member supported in the central bore above the tubing hanger and through which passes the production bore.
 20. 34.The flow completion system of claim 32, wherein the first and second closure members each comprise a wireline deployable plug.
 21. 35.The flow completion apparatus of claim 32, wherein the first closure member comprises a first sealing member which is mounted on a wireline deployable plug body and the second closure member comprises a second sealing member which is mounted on a wireline deployable plug body above the first sealing member.
 22. 36.The flow completion system of claim 32, further comprising: an ancillary bore which extends generally axially through the tubing hanger assembly from a lower end to an upper end of the tubing hanger assembly; and an ancillary closure member which is positioned in the ancillary bore.
 23. 37.The flow completion system of claim 36, wherein: the ancillary bore includes a generally lateral branch with a valve that is moveable to open and close the lateral branch.
 24. 38.The flow completion system of claim 32 further comprising a tree cap which comprises: an annular body; and means for securing the body to the tubing spool.
 25. 39.The flow completion system of claim 32, further comprising a connector with a seal stab for engaging the ancillary bore.
 26. 40.The flow completion system of claim 39, wherein the connector further comprises: a fluid bore extending through the connector and which is adapted to be connected to a conduit; and the fluid bore communicating with a bore in the seal stab; wherein fluid communication may be established between the ancillary bore and the conduit through the seal stab.
 27. 41.The flow completion system of claim 32, further comprising: a blowout preventer which is removably connectable to the top of the tubing spool and which includes a blowout preventer bore, a set of blowout preventer rams, and at least one choke and kill line that communicates with a portion of the blowout preventer bore which is located adjacent the blowout preventer rams; and a tubing hanger tool which is removably connectable to the top of the tubing hanger assembly and which includes a cylindrical outer surface portion and a flowbore that communicates with the production bore; an annulus passageway which communicates the tubing annulus with the outer surface portion; wherein the blowout preventer rams are adapted to sealingly engage the outer surface portion above the annulus passageway; whereby fluid communication between the tubing annulus and the blowout preventer choke and kill line may be established through the annulus passageway and the portion of the blowout preventer bore which is located below the blowout preventer rams.
 28. 42.The flow completion apparatus of claim 32, further comprising: a tubing hanger tool which is removably connectable to the top of the tubing hanger assembly in a predetermined orientation; the tubing hanger tool including a flow passageway therethrough and being sealed to the tubing spool; and the tubing hanger tool having stabs received by the production bore and the ancillary bore in the tubing hanger assembly.
 29. 43.The flow completion apparatus of claim 42 wherein the flow passageway extends through one of the stabs for flow communication with the production bore or ancillary bore.
 30. 44.A well production assembly located at an upper end of a string of tubing extending into a well, comprising: a production tree having a longitudinal axis, an axial bore and a lateral production passage, the lateral production passage having an inlet at the bore and extending laterally through a sidewall of the production tree; a tubing hanger landed in the axial bore and adapted to be located at an upper end of a string of tubing, the tubing hanger having a co-axial production passage co-axial with the production tree axial bore and extending axially through the tubing hanger and the tubing hanger having a lateral production passageway which extends laterally from the co-axial production passage through the tubing hanger and has an outlet at the exterior of the tubing hanger which registers with the inlet of the lateral production passage of the production tree; the tubing hanger having an offset vertical passage extending through the tubing hanger from a lower end to an upper end of the tubing hanger offset from the co-axial production passage, the offset vertical passage having a lower end adapted to be in communication with a tubing annulus surrounding the string of tubing; a first closure member installed in the co-axial production passage above the lateral production passageway of the tubing hanger; and a second closure member installed in the offset vertical passage.
 31. 45.The well production assembly according to claim 44, further comprising: a removable internal tree cap which sealingly engages the bore of the tree above the tubing hanger, the tree cap having first and second vertical passages which are offset from and parallel to each other, the first vertical passage of the tree cap aligning with the co-axial production passage of the tubing hanger, the second vertical passage of the tree cap aligning with the offset vertical passage of the tubing hanger; a third closure member installed in the first vertical passage of the tree cap; and a fourth closure member installed in the second vertical passage of the tree cap.
 32. 46.The well production assembly according to claim 44, further comprising: a lateral flow passage extending laterally from the offset vertical passage through the tubing hanger and having an opening at the exterior of the tubing hanger; and a tree flow passage having an opening in the axial bore of the tree and extending laterally through the tree for sealingly registering with the opening of the lateral flow passage of the tubing hanger.
 33. 47.A well production assembly located at an upper end of a string of tubing extending into a well, comprising: a production tree having a longitudinal axis, an axial bore and first and second lateral passages, the first and second lateral passages having an inlet at the bore and extending laterally through a sidewall of the production tree; a tubing hanger landed in the axial bore and adapted to be located at an upper end of a string of tubing, the tubing hanger having a co-axial production passage co-axial with the production tree axial bore and extending axially through the tubing hanger and the tubing hanger having a first lateral passageway which extends laterally from the co-axial production passage through the tubing hanger and has an outlet at the exterior of the tubing hanger which registers with the inlet of the first lateral passage of the production tree; the tubing hanger having an offset passage extending through the tubing hanger from a lower end to an upper end of the tubing hanger offset from the co-axial production passage and a second lateral passageway which extends laterally from the offset vertical passage through the tubing hanger and has an outlet at the exterior of the tubing hanger which registers with the inlet of the second lateral passage of the tree; a first closure member installed in the co-axial production passage above the first lateral passage of the tubing hanger; and a second closure member installed in the offset passage above the second lateral passageway of the tubing hanger.
 34. 48.A well production assembly comprising in combination: a production tree having a vertical axis, an axially extending bore, and a lateral production passage extending from the bore through a sidewall of the tree transverse to the vertical axis; a shoulder formed on the tree; a tree auxiliary passage extending through the sidewall of the tree and having an auxiliary connector located at the shoulder; a string of tubing extending into a well; a tubing hanger which lands sealingly in the bore and is connected to the string of tubing, the tubing hanger having a lateral production passage extending from a co-axial production passage co-axial with the axially extending bore and extending axially through the tubing hanger, the lateral production passage aligning with the lateral production passage of the tree; and a mandrel disposed in the wellhead and having a mandrel auxiliary passage extending therethrough, the auxiliary connector in the tree sealingly mating with the auxiallry passage when the tree lands on the wellhead to communicate the tree auxiliary passage with the mandrel auxiliary passage.
 35. 49.The well production assembly of claim 48 wherein the mandrel auxiliary passage is used to test seals between the wellhead and spool tree.
 36. 50.The well production assembly of claim 48 wherein the tubing hanger has an offset vertical passage extending through the tubing hanger from a lower end to an upper end of the tubing hanger offset from the co-axial production passage and a lateral flow passageway which extends laterally from the co-axial production passageway through the tubing hanger and has an outlet at the exterior of the tubing hanger which registers with the inlet of a lateral flow passage in the tree.
 37. 51.In a subsea wellhead system having a wellhead housing secured to a first string of casing, a production casing hanger having an interior surface and an exterior surface and landed in the wellhead housing and secured to a production casing inside the first string of casing and extending below the production casing hanger, a casing hanger packoff that seals between the exterior surface on the production casing hanger and the wellhead housing, and a tree assembly that lands on the wellhead and has an axial bore, the improvement comprising: a casing hanger communication passage passing through the production casing hanger and by-passing the production casing hanger packoff; and a port closure sleeve releasably secured to the production casing hanger to open and close the communication passage.
 38. 52.A wellhead assembly comprising: a wellhead housing; a spool tree fixed and sealed to the housing, and having at least a lateral production fluid outlet port connected to a valve; a production casing hanger carried in the housing below the spool tree; an isolation sleeve which is sealed at its lower end to the production casing hanger and at its upper end to the spool tree to define an annular void between the isolation sleeve and the housing; and an adapter located in the annular void and providing part of a passage from a production casing annulus to a production casing annulus pressure monitoring port in the spool tree, the adapter having a valve for opening and closing the passage, the valve being operable through the spool tree when the isolation sleeve is uninstalled in the spool tree.
 39. 53The wellhead assembly of claim 52 further including: a tubing hanger landed within the spool tree at a predetermined angular position at which a lateral production fluid outlet port in the tubing hanger is in alignment with that in the spool tree; the tubing hanger and spool tree having complementary guide means to rotate the tubing hanger into the predetermined angular position relatively to the spool tree as the tubing hanger is lowered onto its landing, the guide means being provided by complementary oblique edge surfaces, one facing downwards on an orientation sleeve depending from the tubing hanger and the other facing upwards on an orientation sleeve carried by the spool tree.
 40. 54.A subsea well assembly for a cased well, the assembly comprising: a wellhead housing landing in the cased well and having a string of outer casing extending therefrom; at least one casing hanger landing in the wellhead housing which is secured to a string of inner casing, defining a casing annulus surrounding the inner casing; a seal located around an upper portion of the casing hanger to sealingly connect the casing hanger with an interior wall of the wellhead housing; the interior wall of the wellhead housing forming a passageway from below the seal of the casing hanger to a passageway outlet; and a casing annulus port in communication with the passageway outlet of the passageway for monitoring the casing annulus pressure.
 41. 55.An apparatus supporting a hanger and pipe string from the upper end of a cased well, the apparatus comprising: a mandrel adapted to be fixed and sealed to the upper end of the cased well, said mandrel having a mandrel bore therethrough adapted to receive the hanger and pipe string, said mandrel forming a wall with a sealing surface adapted to sealingly engage seals between said wall and the hanger; and said wall having a fluid passageway therethrough extending from an opening in the mandrel wall below said sealing surface to an opening in the mandrel wall above said sealing surface.
 42. 56.The apparatus of claim 55 further including a valve disposed in said fluid passageway.
 43. 57.An assembly for supporting pipe from a subsea wellhead, the assembly comprising: a mandrel adapted to be fixed and sealed to the wellhead, said mandrel having a mandrel bore therethrough forming a mandrel wall; a hanger having a hanger bore and being landed within said mandrel bore, said hanger supporting the pipe and forming a pipe annulus; hanger seals sealing between said mandrel wall and said hanger to form an upper mandrel bore portion; and a loop line extending from the pipe annulus, through an opening in said mandrel wall, through a passageway in said mandrel wall, and through an opening in said mandrel wall at said upper mandrel bore portion, said loop line allowing selective fluid circulation between the pipe annulus and said upper mandrel bore portion.
 44. 58.An apparatus for supporting a hanger and pipe string from the upper end of a cased well, the pipe string forming an annulus between the pipe string and cased well, the apparatus comprising: a mandrel adapted to be fixed and sealed to the upper end of the cased well, said mandrel having a mandrel bore therethrough receiving the hanger and pipe string, said mandrel forming a wall with inner and outer surfaces; said inner surface of said mandrel adapted to have sealing engagement with seals sealing the hanger; said wall having a fluid passageway therethrough extending from an opening in said mandrel wall below the sealing engagement to an opening in the mandrel wall above the sealing engagement; and said passageway adapted to provide fluid communication between the annulus and that portion of the mandrel bore above the sealing engagement.
 45. 59.An apparatus for monitoring a casing annulus in a well, the casing annulus being formed by an outer casing supported by a wellhead housing and an inner casing suspended within the outer casing by a casing hanger, the casing hanger being supported by the wellhead housing, the apparatus comprising: an adapter with adapter seals adapted to seal the casing hanger and the wellhead housing; a tree body adapted to be fixed and sealed to the wellhead housing, said tree body having a tree body bore forming a wall with interior and exterior surfaces; a mandrel extending between said tree body and said adapter with mandrel seals adapted to seal with the wellhead housing; a port communicating between said interior and exterior surfaces; and a fluid passageway extending around said adapter seals and mandrel seals and communicating the casing annulus with said port.
 46. 60.The apparatus of claim 59 wherein said port extends through said wall.
 47. 61.The apparatus of claim 59 wherein said passageway extends through said adapter and mandrel.
 48. 62.The apparatus of claim 61 wherein said adapter includes a valve to open and close that portion of said passageway passing through said adapter.
 49. 63.The apparatus of claim 59 wherein said port acts as a vent to relieve pressure in the casing annulus.
 50. 64.An apparatus for monitoring the flow of fluids in a well having an outer casing, comprising: a wellhead supporting a casing hanger suspending an inner casing within the outer casing to form a casing annulus therebetween; a mandrel connected to said wellhead and having a mandrel bore forming a mandrel wall; a sleeve extending from said mandrel and to said casing hanger to form a passage thereamong; said sleeve having a mandrel end seals sealing with said mandrel and a casing hanger end seals sealing with said casing hanger; and a fluid passageway around said casing hanger extending between said casing annulus and that portion of said mandrel bore above said mandrel end seals.
 51. 65.The apparatus of claim 64 further including an annulus passageway extending from said mandrel bore to an annulus port through said mandrel wall.
 52. 66.The apparatus of claim 64 further including a valve in said annulus passageway.
 53. 67.An assembly for supporting tubing within a well having a wellhead housing and for selective use with a blowout preventer having a BOP bore comprising: a subsea tree adapted for disposal below the blowout preventer and fixed and sealed to the wellhead housing, said subsea tree having a wall with a central bore therethrough and a first lateral port connected to a valve, said central bore having an internal surface and adapted to form a common passageway with the BOP bore; a tubing hanger landed and sealed within said subsea tree at a predetermined angular position at which a second lateral port in said tubing hanger is in alignment with said first lateral port in said subsea tree, said tubing hanger supporting the tubing; at least one vertical bore in said tubing hanger being sealed above said second lateral port by a sealing member, and said internal surface of said central bore through said subsea tree being sealed above said tubing hanger by an internal tree cap, said sealing member and internal tree cap being retrievable through the BOP bore; a workover port extending through said wall of said subsea tree for selective fluid circulation with that portion of said common passageway below the BOP bore and above said tubing hanger; and an annulus port extending through said wall of said subsea tree for selective fluid circulation with an annulus around the tubing, said workover and annulus ports being interconnected via a flow passageway having at least one valve.
 54. 68.The assembly of claim 67 wherein said internal tree cap includes a opening therethrough.
 55. 69.The assembly of claim 68 further includes means for opening and closing said opening.
 56. 70.The assembly of claim 69 wherein said means for opening and closing includes a plug.
 57. 71.The assembly of claim 69 wherein a circulation flow path is formed through said internal tree cap opening and said workover port for selective fluid circulation during workover.
 58. 72.The assembly of claim 67 wherein said internal tree cap is removable.
 59. 73.The assembly of claim 67 wherein said internal tree cap is a plug.
 60. 74.The assembly of claim 73 wherein said plug is an internal isolation stopper.
 61. 75.The assembly of claim 74 wherein said plug includes an opening.
 62. 76.The assembly of claim 75 wherein said opening is closed by an in situ wireline activated plug.
 63. 77.The assembly of claim 69 wherein said means for opening and closing is not a valve having a flow bore therethrough which is substantially the same size as the central bore through said subsea tree.
 64. 78.The assembly of claim 67 further including a production fluid flow passage, said production fluid flow passage extending through the tubing, through that tubing hanger portion of said at least one vertical bore of said tubing hanger below said sealing member, through said second lateral port, and through said first lateral port, said production fluid flow passage not including any internal valves.
 65. 79.The wellhead assembly of claim 67 further comprising a bypass flowpath extending from said annulus port, through said flow passageway and said workover port, to said central bore above said tubing hanger.
 66. 80.The wellhead assembly of claim 67, further comprising a crossover flowpath interconnecting said first lateral port and said flow passageway, said crossover flowpath having a crossover valve for controlling flow therethrough.
 67. 81.The wellhead assembly of claim 80 further comprising a first combined workover flowpath extending from said annulus port, through said flow passageway and said crossover flowpath, to said first lateral port.
 68. 82.The wellhead assembly of claim 80 further comprising a second combined workover flowpath extending from said workover port, through said flow passageway and said crossover flowpath, to said first lateral port.
 69. 83.The wellhead assembly of claim 67 wherein said central bore has an inside diameter substantially the same as the diameter of the BOP bore.
 70. 84.An assembly for supporting tubing within a well from a wellhead housing for selective use with a blowout preventer having a BOP bore comprising: a subsea tree adapted for disposal below the blowout preventer and fixed and sealed to the wellhead housing, said subsea tree having a wall with a central bore therethrough and a first lateral port connected to a valve, said central bore having an internal surface and adapted to form a common passageway with the BOP bore; a tubing hanger landed and sealed within said subsea tree at a predetermined angular position at which a second lateral port in said tubing hanger is in alignment with said first lateral port in said subsea tree, said tubing hanger supporting the tubing; at least one vertical bore in said tubing hanger; a workover port extending through said wall of said subsea tree for selective fluid circulation with that portion of said common passageway below the BOP bore and above said tubing hanger; and an annulus port extending through said wall of said spool tree for selective fluid circulation with an annulus around the tubing, said workover and annulus ports being interconnected via a flow passageway having at least one valve.
 71. 85.The assembly of claim 84 wherein said valve is external to said subsea tree.
 72. 86.The assembly of claim 84 further including a casing annulus passageway having an internal valve.
 73. 87.The assembly of claim 84 further including a running tool supporting an internal tree cap, said internal tree cap having an opening therethrough and being received by said central bore above said tubing hanger.
 74. 88.The assembly of claim 87 wherein a circulation flowpath is formed through said running tool, said opening, said tubing hanger and the tubing for selective circulation downhole.
 75. 89.The assembly of claim 87 wherein said opening may opened and closed remotely.
 76. 90.The assembly of claim 87 further including a sealing member having seals therearound to sealingly engage said internal surface of said central bore through said subsea tree to seal said central bore above said tubing hanger.
 77. 91.The assembly of claim 90 wherein said sealing member has an aperture therethrough.
 78. 92.The assembly of claim 90 wherein said sealing member is removable through the BOP bore.
 79. 93.An assembly for supporting pipe in a well and for selective use with a blowout preventer having a BOP bore, the assembly having a subsea wellhead, the assembly comprising: a mandrel adapted to be disposed below the blowout preventer and fixed and sealed to the wellhead, said mandrel having a mandrel bore therethrough forming a mandrel wall with a mandrel lateral production passageway extending through said wall; a hanger having a hanger bore and a hanger lateral production passageway, the hanger being landed within said mandrel bore with said hanger lateral production passageway being in flow communication with said mandrel lateral production passageway, said hanger supporting the pipe and forming a pipe annulus; hanger seals sealing between said mandrel wall and said hanger to form an upper mandrel bore portion, said upper mandrel bore portion being adapted to form a common passageway with the BOP bore, said hanger seals sealing off said mandrel and hanger lateral production passageways from said common passageway; a loop line extending from the pipe annulus, through an opening in said mandrel wall, through a passageway in said mandrel wall, and through an opening in said mandrel wall to said upper mandrel bore portion, said loop line allowing selective fluid circulation between said pipe annulus and said common passageway.
 80. 94.The assembly of claim 93 further including a first plug received by said hanger bore to seal said hanger bore above said hanger lateral production passageway.
 81. 95.The assembly of claim 94 further including a second plug received by said mandrel bore to seal said upper mandrel bore portion above said hanger seals.
 82. 96.The assembly of claim 95 wherein said first plug and said second plug are passable through the BOP bore.
 83. 97.The assembly of claim 95 said second plug includes external seals that sealingly engage said mandrel wall.
 84. 98.An assembly for supporting tubing within a well from a subsea wellhead for selective use with a blowout preventer having a BOP bore, the assembly comprising: a mandrel adapted to be disposed below the blowout preventer and fixed and sealed to the wellhead, said mandrel having a mandrel vertical bore therethrough forming a mandrel wall with a mandrel lateral production passageway extending through said wall, said mandrel bore having an internal surface; a tubing hanger having a hanger vertical bore and a hanger lateral production passageway, the hanger being landed within said mandrel vertical bore with said hanger lateral production passageway being in flow communication with said mandrel lateral production passageway, said hanger supporting the tubing forming a tubing annulus; hanger seals sealing between said mandrel wall and said hanger to form a mandrel non-production flow bore above said hanger seals, said mandrel non-production flow bore being adapted to form a common passageway with the BOP bore, said hanger seals sealing off said mandrel and hanger lateral production passageways from said mandrel non-production flow bore and the common passageway; a circulation passageway extending from the pipe annulus, through an opening in said mandrel wall below said hanger seals, through a passageway in said mandrel wall, and through an opening in said mandrel wall above said hanger seals to said mandrel non-production flow bore, said circulation passageway allowing selective fluid circulation between said pipe annulus and said mandrel non-production flow bore and the common passageway; a first plug sealing said hanger vertical bore above said hanger lateral production bore; and a second plug sealing said mandrel non-production flow bore above said tubing hanger.
 85. 99.An apparatus for use selectively with a blowout preventer for controlling the flow of fluids in a well comprising: a subsea tree adapted for disposal below the blowout preventer, said subsea tree having a central bore formed by a wall of said subsea tree and a production passageway, an annulus passageway, and a workover passageway in said wall, said workover passageway extending laterally into said central bore; a production valve disposed with said subsea tree for controlling flow through said production passageway; an annulus valve disposed with said subsea tree for selective fluid circulation downhole through said annulus passageway; a workover valve disposed with said subsea tree for selective fluid circulation through said workover passageway; a tubing hanger supported and sealed within said subsea tree and suspending tubing in the well, said tubing hanger and tubing having a flowbore and forming an annulus in the well, said tubing hanger having an aperture communicating said flowbore with said production passageway, and said annulus passageway communicating with said annulus; said workover passageway in fluid communication with said subsea tree central bore above said tubing hanger; said annulus passageway in fluid communication with said workover passageway; said production passageway in fluid communication with said annulus passageway and workover passageway; a crossover valve for controlling fluid flow between said production passageway and said annulus passageway or workover passageway; and fluid circulation paths being formed between said subsea tree central bore, workover passageway, and annulus passageway to selectively circulate downhole using said tubing flowbore and tubing annulus.
 86. 100.The apparatus of claim 99 further including a production fluid isolation valve communicating with said production passageway and an annulus isolation valve communicating with said annulus passageway.
 87. 101.A method for controlling fluid flow in a well comprising: suspending tubing from a tubing hanger; supporting and sealing the tubing hanger within the bore of a subsea tree for selective disposal below a blowout preventer having a BOP bore; forming a common flow passageway between the BOP bore and a portion of the subsea tree bore above the seals around the tubing hanger; extending a tubular member into the BOP bore, attaching the tubular member to the tubing hanger, and closing the blowout preventer therearound; forming a flowpath through the tubing and the tubular member, forming an annular area between the tubular member and the subsea tree in the common flow passageway and forming an annulus around the tubing below the tubing hanger; forming a production passageway through the tubing, through a lateral port in the tubing hanger and through the wall of the subsea tree; controlling flow through the production passageway by a production valve; forming an annulus passageway from the annulus and through the wall of the subsea tree; controlling flow through the annulus passageway by an annulus valve; forming a workover passageway from the annular area between the tubular member and subsea tree and through the wall of the subsea tree; controlling flow through the workover passageway; providing fluid communication between the workover passageway and the annulus passageway; forming a crossover fluid passageway between the production passageway and annulus passageway; controlling flow through the crossover fluid passageway; and circulating fluid downhole using the flowpath, tubing annulus, annulus passageway, workover passageway, and annular area.
 88. 102.The method of claim 101 further including flowing fluid downhole through the workover passageway, the crossover passageway, and the production passageway.
 89. 103.A method for controlling fluid flow in a well comprising: suspending tubing from a tubing hanger; supporting and sealing the tubing hanger within the bore of a subsea tree for selective disposal below a blowout preventer having a BOP bore; forming a common flow passageway between the BOP bore and a portion of the subsea tree bore above the tubing hanger; forming a flowbore through the tubing and an annulus around the tubing below the tubing hanger; forming a production passageway from the flowbore, through a lateral port in the tubing hanger and through the wall of the subsea tree; controlling flow through the production passageway by a production valve; forming an annulus passageway from the annulus and through the wall of the subsea tree; controlling flow through the annulus passageway by an annulus valve; installing a tubing hanger closure member in the tubing hanger above the production passageway; installing an internal tree cap within the portion of the subsea tree bore above the tubing hanger; forming a workover passageway through the wall of the subsea tree from the bore of the subsea tree above the tubing hanger and between the tubing hanger sealing member and internal tree cap; controlling flow through the workover passageway; forming a crossover fluid passageway between the production passageway and annulus passageway; controlling flow through the crossover fluid passageway; providing fluid communication between the workover passageway and the crossover fluid passageway; and flowing fluid through the production passageway, through the crossover passageway and into the workover passageway between the tubing hanger sealing member and the internal tree cap.
 90. 104.An assembly for use selectively with a blowout preventer for operating a subsea well, comprising: a subsea tree adapted for disposal below the blowout preventer and having a central bore therethrough, a portion of said central bore being formed by an internal generally vertical wall surface, said internal generally vertical wall surface having an opening therein; a tubing hanger assembly mounted and sealed in a predetermined angular position within said central bore of said subsea tree spool body] and suspending tubing within the well, said tubing hanger assembly and tubing forming a central passageway therethrough and an annulus around the tubing below the tubing hanger; a production passageway extending from said central passageway of said tubing hanger assembly into said wall of said subsea tree ; an annulus passageway extending from said annulus around the tubing below the tubing hanger and into said wall of said subsea tree; a workover passageway extending from said opening in said central bore and into said subsea tree, said opening in fluid communication with said central bore above the tubing hanger; and said annulus passageway and workover passageway being in fluid communication through a flowpath to selectively circulate downhole from said central bore of said subsea tree through said workover passageway and annulus passageway with flow through said tubing hanger assembly annulus and central passageway of said tubing hanger assembly.
 91. 105.The assembly of claim 104 further comprising an internal tree cap sealingly disposed within said central bore of said subsea tree to control flow through said central bore.
 92. 106.An assembly for use selectively with a blowout preventer having a BOP bore for operating a subsea well, comprising: a subsea tree adapted for disposal below the blowout preventer and having a generally cylindrical wall forming a central bore therethrough, a portion of said central bore being adapted to form a flow passageway with the BOP bore; a tubing hanger assembly mounted and sealed within said central bore of said subsea tree and suspending tubing within the well, said tubing hanger and tubing forming a central passageway in fluid communication with said central bore of said subsea tree above said tubing hanger assembly and forming an annulus around the tubing below the tubing hanger; a production passageway extending from said central passageway of said tubing hanger assembly into said wall of said subsea tree; an annulus passageway extending from said annulus around the tubing below the tubing hanger and into said wall of said subsea tree; a workover passageway extending from said portion of said central bore of said subsea tree and into said subsea tree wall for fluid communication with said portion of said subsea tree central bore above said tubing hanger; said annulus passageway and workover passageway being in fluid communication through a flowpath outside of said central bore of said subsea tree; a sealing member mounted within said central passageway of said tubing hanger assembly to control flow through said central passageway and through said central bore of said subsea tree; and a sealing member sealed and locked internally of said portion of said central bore above said tubing hanger assembly.
 93. 107.A wellhead for supporting tubing for use selectively with a blowout preventer having a BOP bore, the wellhead including a wellhead housing, the wellhead comprising: a subsea tree adapted for disposal below the blowout preventer and fixed and sealed to the wellhead housing, said subsea tree having a wall with a central bore therethrough and at least a first lateral production fluid outlet port connected to a valve, a portion of said central bore being adapted to form a common passageway with the BOP bore; a tubing hanger supporting the tubing and landed and sealed within said subsea tree at a predetermined angular position at which a second lateral production fluid outlet port in said tubing hanger is in alignment with said first lateral production fluid outlet port in said subsea; at least one vertical production fluid bore in said tubing hanger being sealed above said second lateral production fluid outlet port by a sealing member, and said portion of said central bore through said spool tree being internally sealed above said tubing hanger by an internal tree cap removable through the BOP bore; a workover port extending at least partially through said wall of said subsea tree from an area in said portion of said central bore between said sealing member and internal tree cap; and a tubing annulus fluid port extending at least partially through said wall of said spool tree from an annulus formed around the tubing; said workover and tubing annulus ports in said subsea tree being interconnected via a passageway having at least one valve.
 94. 108.A tree system for use selectively with a blowout preventer having a BOP bore for a subsea well, comprising: a subsea tree having a bore therethrough, a portion of said bore being adapted to form a flow passageway with the BOP bore upon installing the blowout preventer above said spool tree; a tubing hanger suspending tubing and supported by said subsea tree, seals sealing between said tubing hanger and said subsea tree, said tubing hanger and tubing having an internal production bore extending downwardly into the well and forming a tubing annulus extending downwardly into the well; said subsea tree and tubing hanger forming a lateral production flowpath in fluid communication with said internal production bore and having a production control valve for opening and closing said lateral production flowpath to control flow therethrough; said subsea tree forming an annulus flowpath in fluid communication with said tubing annulus and having an annulus control valve controlling flow therethrough; said subsea tree having a workover flowpath through the wall of the subsea tree communicating with said portion of said subsea tree bore above said seals and having a workover valve controlling flow therethrough; a circulation flowpath being formed through said internal production bore of said tubing hanger with said lateral production flowpath closed and through said tubing annulus to selectively circulate fluid downhole using said internal production bore and said tubing annulus; and said internal production bore above said lateral production flowpath being adapted for isolation from said subsea tree bore portion.
 95. 109.The tree system of claim 108, further comprising: a sealing member mounted in said tubing hanger; and, an internal tree cap sealably mounted completely internal of said portion of said bore of said spool tree.
 96. 110.The tree system of claim 109, wherein a fluid passageway is formed above said sealing member for selective fluid circulation.
 97. 111.The tree system of claim 109, further including a first external flowpath with a tubing annulus valve for controlling flow therethrough, a second external flowpath with a production fluid isolation valve for controlling flow therethrough, and a fluid passageway formed between said first and second external flowpaths by said annulus flowpath, tubing annulus, production bore, and production flowpath.
 98. 112.A tree system for use selectively with a blowout preventer having a BOP bore, a tubular member extending through the BOP bore and having a fluid bore, and a wellhead for a subsea well, comprising: a subsea tree for installation on the wellhead, said subsea tree having a wall with a bore therethrough, a portion of said bore being adapted to form a flow passageway with the BOP bore upon installation of the blowout preventer above said subsea tree; a tubing hanger suspending tubing and supported by said subsea tree, seals sealing between said tubing hanger and said subsea spool tree, said tubing hanger and tubing having an internal production bore and forming a tubing annulus extending downwardly into the well, said internal production bore adapted for connection with the tubular member for fluid communication with the fluid bore of the tubular member; said subsea tree and tubing hanger forming a lateral production flowpath in fluid communication with said internal production bore and having a production control valve controlling flow therethrough; said subsea tree forming an annulus flowpath in fluid communication with said tubing annulus and having an annulus control valve controlling flow therethrough; said subsea tree having a workover flowpath through the wall of the subsea tree communicating with said portion of said subsea spool tree bore above said seals and having a workover valve controlling flow therethrough; a circulation flowpath being formed upon establishing fluid communication between said internal production bore of said tubing hanger and tubing and fluid bore of said tubular member, said circulation flowpath allowing flow through said internal production bore of said tubing hanger and tubing and fluid bore of said tubular member and through said annulus and annulus flowpath for selective fluid circulation through said circulation flowpath; a workover/annulus flow connection interconnecting said workover flowpath and said annulus flowpath for selective fluid circulation downhole through said circulation flowpath and said workover flowpath to an annular area formed between the tubular member and subsea tree bore.
 99. 113.The tree system of claim 112 further comprising a bypass flowpath extending from said annulus flowpath, through said workover/annulus flow connection and said workover flowpath, to said portion of said subsea tree bore.
 100. 114.The tree system of claim 112, further comprising a crossover flowpath interconnecting said production flowpath and said workover/annulus flow connection, said crossover flowpath having a crossover valve for controlling flow therethrough.
 101. 115.The tree system of claim 114 further comprising a first combined workover flowpath extending from said annulus flowpath, through said workover/annulus flow connection and said crossover flowpath, to said production flowpath.
 102. 116.The tree system of claim 114 further comprising a second combined workover flowpath extending from said workover flowpath, through said workover/annulus flow connection and said crossover flowpath, to said production flowpath.
 103. 117.A tree system for a wellhead for the completion and work-over of a subsea well, comprising: a subsea tree having a bore and for installation on the wellhead; a tubing hanger suspending tubing and supported by said subsea tree, seals sealing between said tubing hanger and said subsea tree, said tubing having an internal production bore and forming a tubing annulus extending downwardly into the well; said subsea tree and tubing hanger forming a production flowpath in fluid communication with said internal production bore and having a production control valve controlling flow therethrough; said subsea tree forming an annulus flowpath in fluid communication with said tubing annulus and having an annulus control valve controlling flow therethrough; a drilling blowout preventer having a BOP bore and a member for closing said BOP bore, a portion of said subsea tree bore adapted to form a flow passageway with said BOP bore; said subsea tree having a workover flowpath communicating with said subsea tree bore portion above said seals and below said BOP bore and having a workover valve controlling flow therethrough; choke and kill lines connected to said drilling blowout preventer for communicating said BOP bore with the surface; and a tubular member extending to the surface and in fluid communication with said tubing hanger, said tubular member forming a common bore communicating with said internal production bore for selective fluid circulation downhole using said internal production bore and tubing annulus in conjunction with at least one of said choke and kill lines extending from the BOP to the surface.
 104. 118.The tree system of claim 117, wherein one of said choke and kill lines forms a passageway from the surface to said BOP bore above said tubing hanger.
 105. 119.The tree system of claim 117 further comprising a workover/annulus flow connection interconnecting said workover flowpath and said annulus flowpath for selective fluid communication.
 106. 120.The spool tree system of claim 119, further comprising a crossover flowpath interconnecting said production flowpath and said workover/annulus flow connection, said crossover flowpath having a crossover valve for controlling flow therethrough.
 107. 121.A tree system for a wellhead for the completion and work-over of a subsea well, comprising: a subsea tree having a bore and for installation on the wellhead; a tubing hanger suspending tubing and supported by said subsea tree, seals sealing between said tubing hanger and said subsea tree, said tubing having an internal production bore and forming a tubing annulus extending downwardly into the well; said subsea tree and tubing hanger forming a production flowpath in fluid communication with said internal production bore and having a production control valve controlling flow therethrough; said subsea tree forming an annulus flowpath in fluid communication with said tubing annulus and having an annulus control valve controlling flow therethrough; a drilling blowout preventer having a BOP bore and a member for closing said BOP bore, a portion of said subsea tree bore adapted to form a flow passageway with said BOP bore; said subsea tree having a workover flowpath communicating with said subsea tree bore portion above said seals and below said BOP bore and having a workover valve controlling flow therethrough; choke and kill lines connected to said drilling blowout preventer for communicating said BOP bore with the surface; a pipe string extending to the surface and in fluid communication with said tubing hanger, said pipe string forming a common bore communicating with said internal production bore; a workover/annulus flow connection interconnecting said workover flowpath and said annulus flowpath; and a fluid passageway to the surface being formed by said common bore, production bore, tubing annulus, annulus flowpath, workover/annulus flow connection, workover flowpath, BOP bore, and one of said choke and kill lines.
 108. 122.A tree system for a wellhead for the completion and work-over of a subsea well, comprising: a subsea tree having a bore and for installation on the wellhead; a tubing hanger suspending tubing and supported by said subsea tree, seals sealing between said tubing hanger and said subsea tree, said tubing having an internal production bore and forming a tubing annulus extending downwardly into the well; said subsea tree and tubing hanger forming a production flowpath in fluid communication with said internal production bore and having a production control valve controlling flow therethrough; said subsea tree forming an annulus flowpath in fluid communication with said tubing annulus and having an annulus control valve controlling flow therethrough; a drilling blowout preventer having a BOP bore and a member for closing said BOP bore, a portion of said subsea tree bore adapted to form a flow passageway with said BOP bore; said subsea tree having a workover flowpath communicating with said subsea tree bore portion above said seals and below said BOP bore and having a workover valve controlling flow therethrough; choke and kill lines connected to said drilling blowout preventer for communicating said BOP bore with the surface; a workover/annulus flow connection interconnecting said workover flowpath and said annulus flowpath; a pipe string extending to the surface and in fluid communication with said tubing hanger, said pipe string forming a common bore communicating with said internal production bore; a crossover flowpath interconnecting said production flowpath and said workover/annulus flow connection, said crossover flowpath having a crossover valve for controlling flow therethrough; and a fluid passageway being formed by said common bore, internal production bore, tubing annulus, annulus flowpath, workover/annulus flow connection, crossover flowpath, and production flowpath.
 109. 123.A tree system for a wellhead for the completion and work-over of a subsea well, comprising: a subsea tree having a bore and for installation on the wellhead; a tubing hanger suspending tubing and supported by said subsea tree, seals sealing between said tubing hanger and said subsea tree, said tubing having an internal production bore and forming a tubing annulus extending downwardly into the well; said subsea tree and tubing hanger forming a production flowpath in fluid communication with said internal production bore and having a production control valve controlling flow therethrough; said subsea tree forming an annulus flowpath in fluid communication with said tubing annulus and having an annulus control valve controlling flow therethrough; a drilling blowout preventer having a BOP bore and a member for closing said BOP bore, a portion of said subsea tree bore adapted to form a flow passageway with said BOP bore; said spool tree having a workover flowpath communicating with said subsea tree bore portion above said seals and below said BOP bore and having a workover valve controlling flow therethrough; choke and kill lines connected to said drilling blowout preventer for communicating said BOP bore with the surface; a workover/annulus flow connection interconnecting said workover flowpath and said annulus flowpath; a pipe string extending to the surface and in fluid communication with said tubing hanger, said pipe string forming a common bore communicating with said internal production bore; a crossover flowpath interconnecting said production flowpath and said workover/annulus flow connection, said crossover flowpath having a crossover valve for controlling flow therethrough; and a fluid passageway being formed by one of said choke and kill lines, workover flowpath, workover/annulus flow connection, crossover flowpath, production flowpath, and common bore.
 110. 124.A tree system for a wellhead for the completion and work-over of a subsea well, comprising: a subsea tree having a bore and for installation on the wellhead; a tubing hanger suspending tubing and supported by said subsea tree, seals sealing between said tubing hanger and said spool tree, said tubing having an internal production bore and forming a tubing annulus extending downwardly into the well; said subsea tree and tubing hanger forming a production flowpath in fluid communication with said internal production bore and having a production control valve controlling flow therethrough; said subsea tree forming an annulus flowpath in fluid communication with said tubing annulus and having an annulus control valve controlling flow therethrough; a drilling blowout preventer having a BOP bore and a member for closing said BOP bore, a portion of said subsea tree bore adapted to form a flow passageway with said BOP bore; said subsea tree having a workover flowpath communicating with said subsea tree bore portion above said seals and below said BOP bore and having a workover valve controlling flow therethrough; choke and kill lines connected to said drilling blowout preventer for communicating said BOP bore with the surface; a pipe string extending to the surface and in fluid communication with said tubing hanger, said pipe string forming a common bore communicating with said internal production bore; a workover/annulus flow connection interconnecting said workover flowpath and said annulus flowpath; and said member being closed around said pipe string and further comprising a fluid passageway extending from the surface to the BOP bore through one of said choke and kill lines, another fluid passageway extending from the surface through said common bore, internal production bore, tubing annulus, annulus flowpath, workover/annulus flow connection, and workover flowpath to the BOP bore, and the other of said choke and kill lines extending from the BOP bore to the surface.
 111. 125.An assembly for use selectively with a blowout preventer having a BOP bore for operating a subsea well, comprising: a subsea body adapted for disposal below the blowout preventer and having a generally cylindrical internal wall forming a subsea body central bore therethrough, a portion of said central bore being adapted to form a flow passageway with the BOP bore; a tubing hanger assembly mounted in said spool body central bore and having a central passageway with a production passageway extending from said tubing hanger central passageway, an annulus being formed around said tubing hanger assembly; said internal wall of said subsea body having a production port in fluid communication with said production passageway, an annulus port in fluid communication with said annulus, and a workover port in fluid communication with said portion of said subsea body central bore above said production passageway; and said annulus port and said workover port being in fluid communication externally of said spool body central bore.
 112. 126.A wellhead system comprising: a wellhead; an inner casing suspended within said wellhead and forming a casing annulus with an outer casing; a mandrel disposed on said wellhead and having a bore therethrough; tubing insertable through said bore and suspended within said mandrel and said inner casing, said tubing having a flowbore and forming a tubing annulus with said inner casing; a first valve on said mandrel for controlling flow through said tubing flowbore; a second valve on said mandrel for controlling flow through said casing annulus; a flow passageway from said casing annulus to said bore; and a valve member disposed in said flow passageway for controlling flow through said casing annulus.
 113. 127.An assembly for a subsea well, comprising: a subsea tree having a generally cylindrical internal wall forming an internal bore therethrough and a production port extending laterally through said wall in communication with said internal bore, said internal wall including a landing arranged to support a tubing hanger, with said production port arranged in use to communicate with a lateral production fluid outlet port in the tubing hanger, said tubing hanger having seals for sealing said production port in use between the tubing hanger and the internal wall; a workover port extending laterally from an opening in said internal wall above said production port said opening of said workover port in said internal wall being located in use above said seals; a tubing annulus port extending from an opening in said subsea tree below said production port; and said tubing annulus port and workover port being arranged to be in fluid communication externally of said internal bore.
 114. 128.The assembly according to claim 127, wherein said internal wall includes a profile above said production port arranged to receive an internal tree cap.
 115. 129.he assembly according to claim 127, wherein said subsea tree includes a profile adjacent one end of said internal bore arranged to receive a closure cap.
 116. 130.The assembly according to claim 127, wherein said tubing annulus port and said workover port are in communication with said internal bore via an external loop line.
 117. 131.The assembly according to claim 127, wherein said internal wall includes a landing shoulder arranged to support an orientation member.
 118. 132.The assembly according to claim 127, further including a tubing hanger and production tubing, the tubing hanger having a production bore in communication with the production tubing, with said lateral production port extending from said tubing hanger production bore, said production tubing forming a tubing annulus therearound, and said tubing annulus port being in fluid communication with the production tubing annulus, whereby a flowpath is formed from said opening of said workover port, through said workover port and said tubing annulus port to said production tubing annulus.
 119. 133.The assembly according to claim 127, further including a blowout preventer having a BOP bore and a member for closing the BOP bore with said subsea tree arranged below the blowout preventer and a portion of said internal bore of said subsea tree being arranged to form a flow passageway with the BOP bore.
 120. 134.The assembly according to claim 133, wherein said subsea tree is arranged to receive a tool through the flow passageway for connection to the tubing hanger for flow communication to the surface.
 121. 135.The assembly according to claim 133, wherein the internal wall is arranged to form an annular area around the tool upon closing the BOP bore, allowing selective fluid circulation through the annular area.
 122. 136.The assembly according to claim 135, wherein the blowout preventer has choke and kill lines communicating the BOP bore with the surface; a first flow path being arranged from the surface through tool, tubing hanger, and production tubing; and a second flow path being arranged through the production tubing annulus, tubing annulus port, workover port, annular area and the choke and kill lines to the surface.
 123. 137.The assembly according to claim 127, further comprising a wellhead housing; said spool tree body being fixed and sealed to the housing and said internal bore communicating with at least said production port connected to a valve; and a tubing hanger landed within the subsea tree at a predetermined angular position at which a lateral production port in the tubing hanger is in alignment with the production port in the subsea tree; wherein at least one vertical production bore in the tubing hanger is sealed above the respective production port by a sealing member, and said workover port extends laterally through the wall of the subsea tree from above the sealing member.
 124. 138.The assembly according to claim 137, further including a further sealing member sealing the internal bore above the tubing hanger.
 125. 139.The assembly according to claim 138 wherein the sealing member is a wireline plug and the further sealing member is a stopper which contains at least one opening closed by a wireline plug.
 126. 140.The assembly according to claim 139 wherein the workover port extends laterally through the wall of the subsea tree between the sealing members. 